The present invention relates to the treatment and purification of waste water at high flow rates. More particularly, the present invention relates to process and apparatus for removing animal processing contaminants and fats, oils and greases (xe2x80x9cFOGxe2x80x9d) from large volume quantities of waste water.
Many animal processing operations generate extremely large quantities of water containing contaminant and FOG. For example, cattle processing plants are known to generate up to 2,000 gallons per minute (xe2x80x9cgpmxe2x80x9d) of water or more. Often this water contains biological and chemical contaminant and FOG which must be removed from water before it can be safely discharged into the environment.
Current techniques for treating animal processing waste water include screening and flotation. Such systems are able to demonstrate 70-80% compliance to discharge regulations. For example, biologic oxygen demands (xe2x80x9cBODxe2x80x9d) and chemical oxygen demand (xe2x80x9cCODxe2x80x9d) requirements for discharge into the environment is less than 1,000 parts per million (xe2x80x9cppmxe2x80x9d).
The most common system for treating animal processing waste water is generally referred to as dissolved air flotation (xe2x80x9cDAFxe2x80x9d). This system uses a combination of dissolved air and chemistry to float the contaminants and to remove them via skimming of the solids from the surface. The solids retrieved from this process are not renderable, or usable again. Rather, the solids are wasted and applied to the land. The processing plant must pay to have these solids removed from the premises.
Another less used system is microbial, which uses microbes to digest the contaminants and thus render them harmless and non-contributory to the loading (i.e., BOD or COD) and total suspended solids (xe2x80x9cTSSxe2x80x9d) from the waste stream. This process is time consuming and costly and the flux or amount of through put of waste water is limited.
Filters have been used to remove animal processing contaminants and FOG from waste water. However, traditional microfiltration membranes had a pore size of approximately 5.0 microns with a flex rate of 50-100 gallons per square foot of membrane per day (xe2x80x9cGFDxe2x80x9d). At this flux rate, it would be necessary to have membrane of at least 360,000 square feet to process 2,500 gpm of waste water. If the waste water flow rate is 5,000 gpm, then the membrane size would need to be at least 720,000 square feet. Such membrane sizes are prohibitively large and expensive. Therefore, there exists a need in the art to provide a process and a system for removing animal processing contaminants and FOG from large quantities of waste water and overcoming the aforementioned disadvantages. It would be a major advancement in the art to provide such a process and system which does not require a large footprint (are required for operation). It would also be an important advancement in the art to provide such a process and system which consistently complies with environmental discharge requirements. Such processes and system are disclosed and claimed herein.
The present invention is directed to a process for removing animal contaminants, such as animal waste, blood, tissue, washing solutions, etc. in the presence of high fats, oils and greases from large volumes of waste water and reclaiming the solids in a form acceptable to rendering of the solids. The present invention can readily be adapted for removing other food processing contaminants found in waste water by using suitable oxidation, polymeric and coagulant chemistry. The oxidant reacts with the contaminants and FOG to break down proteins. The polymeric compound dissociates and binds to suspended contaminant and FOG solids to form a first particulate having a size approximately in the range of 15-50 microns. The coagulant reacts with the first particulate to form a second particulate having a size greater than 50 microns.
Known and novel oxidants, polymers and coagulants are available to achieve the desired particulate formation. For instance, sodium hypochlorite, ozone, peroxides, potassium hypo chloride and chlorine dioxide are well-known oxidants. Aluminum chlorohydrate, polyaluminum chloride, calcium aluminate and sodium aluminate are well-known in organic coagulants organic and polymeric coagulants can also be used, such as anionic polyacrylamide, cationic polyamine can also be used. The stoichimetric ratio of coagulant to contaminate is preferably optimized result in acceptable removal at minimum coagulant cost. The required coagulant concentration will depend on several factors, including contaminant influent concentration, waste water flow rate, contaminate effluent compliance requirement, coagulant/contamination reaction connectics, etc.
Treated waste water is passed through a microfiltration membrane which physically separates the contaminants and FOG from the waste water. Suitable microfiltration membranes are commercially available for manufacture such as W. L. Gore and National Filter Media. For instance, one GOR-TEX(copyright) membrane used in the present invention is made from polypropylene felt with a sprayed coating of Teflon. The Teflon coating is intended to promote water passage through the membrane. Such microfiltration membrane material has been found to be useful for many waste water treatment systems. The microfiltration membrane may also be comprised of a polyethylene membrane mounted to a polypropylene or polyethylene felt backing. These membrane materials have also been found to be useful for many waste water treatment systems.
The microfiltration members are used in a tubular xe2x80x9csockxe2x80x9d configuration to maximize surface area. The membrane sock is placed over a slotted tube to prevent the sock from collapsing during use. A net material is placed between the membrane sock and the slotted tube to facilitate flow between the membrane and the slots of the tube. In order to achieve the extremely high volume flow rates, a large number of membrane modules, each containing a number of individual filter socks are used.
The microfiltration membranes preferably have a pore size in the range of 0.5 microns to 10 microns. In controlling the ratio of coagulant to contaminant, 99.99% other created particles can be greater than 10 microns. This allows the use of larger pore size microfiltration membranes. It has been found that the treated waste water flow rate through 0.5 micron to 10 microfiltration membranes is at least 250-300 GFD and typically over 750 GFD.
Solids are preferably removed from the membrane surface by periodically backflushing the microfiltration membranes and draining the filtration vessel within which the membranes are located. The periodic, short duration backflush removes any buildup of contaminants from the walls of the microfiltration membrane socks. The dislodged solid material within the filtration vessel is flushed into a holding tank for further processing of the solids.
The waste water treatment system disclosed herein is designed to provide compliance with the animal processing contaminant discharge effluent limits. Waste water pretreatment chemistry for both soluble and insoluble contaminants, allows for the creation of particulates which are efficiently removed by the microfiltration membranes.